https://www.vbulletin.com/forum/showthread.php/406712-Read-Me-First-Upgrade-Issues-and-Restrictions
So, the "upgrade" has to be installed somewhere different to your vB4 install.
Your vB4 add-ons won't work with vB5.
Your styles won't work with vB5.
You can't use your paid subscriptions - they're not supported in vB5 at this time.
The CMS/Article System is not support in vB5.
The infraction system is not supported in vB5.
The FAQ System is not supported in vB5.
There is no member's list in vB5.
A number of features in the Admin CP no longer work.
You cannot turn off Blogs, Social Groups, Albums (
but can "hide" them with permissions!).
You cannot remove the Activity Stream (
but can hide it!).
If you store your attachments and avatars in the file system, you should make sure to back them up. Depending on where you install vBulletin 5 and how you have your path specified in the database,
you may need to move these files to a new location for them to work properly.
I'm thinking this has been pushed out the door kicking and screaming and leaving fingernail marks in the door frame!!!